Sulfur modified polyvinyl acetate (PVAc)

ABSTRACT

Provided are a sulfur modified polymer composition, free from asphalt, bitumen or like compounds, and method of making same. The inclusion of 50% by weight sulfur, or greater, into the polymer composition results in a composition that is softer and having an increased melting point, relative to the unmodified polymer composition.

RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/596,050 titled “Sulfur Modified Polyvinyl Acetate (PVAc),” filedon Feb. 7, 2012, the disclosure of which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

This invention relates to modified polyvinyl acetate polymer. Moreparticularly, this invention relates to sulfur modified polyvinylacetate polymers, free from asphalt, bitumen or like compounds, havingimproved properties relative to unmodified polyvinyl acetate polymers.

BACKGROUND OF THE INVENTION

Sulfur is a co-product of oil and gas production that is produced inever increasing quantities. For example, sulfur is currently produced ata rate of approximately 10,000 tons/day in Saudi Arabia. The rate ofproduction is expected to increase to 12,000 tons/day in a few years.Although sulfur is a vital resource that is useful for the manufacture amyriad of products, the abundance of sulfur has resulted in worldwidereduction of its price. As worldwide sulfur supplies increase, thestorage of the sulfur will present an environmental hazard. New uses ofsulfur present one solution to the problem of storing the vastquantities of sulfur.

Previous studies relating to the degradation of PVAc in vacuum using TGArevealed a two stage decomposition. The first mass loss commenced atabout 250° C. and continued to about 375° C., after which an inflexionpreceded the second and final mass loss that ultimately led to completedecomposition of the polymer. The first mass loss stage was assignedmainly to the release of acetic acid and simultaneous formation ofdouble bonds in the polymer backbone. The formation of both acetic acidand trans-vinylene species have been explained by comparison withpyrolytic cis or syn elimination of low molar mass ester modelcompounds. It was found that the addition of free radical inhibitors didnot prevent elimination of acetic acid. However, previously studies alsoshowed the formation of several volatile products using free radicalmechanisms. It has also found that the acetic acid generated has acatalytic effect on degradation. This behavior has been compared to thecatalytic effect of HCl on PVC.

Prior investigations have been conducted into inert and oxidativethermal degradation mechanism of PVAc and EVA copolymers usingsemi-crystalline and amorphous EVA having a VA content in the polymerbackbone ranging from about 9 to 73% by weight. More specifically, EVAemulsions of Airflex EN 1035 and Airflex EAF 60 (55 and 60% solids inwater, respectively) from Air Products containing 73 and 60% by weightvinyl acetate were utilized. The thermal study was performed over atemperature range of about 200° C. (to remove water and monomers) toabout 600° C. and 650° C. for inert and oxidative conditionsrespectively. The inert degradation of PVAc as measured using a TGAcoupled with mass spectrometry (TGA-MS) showed two degradation steps:the first and most intense step is deacytelation, which occurs betweenabout 300 and 400° C. The end of the first thermal degradation step ofPVAc in air has been reported to be around 310° C., corresponding to aloss of 95% of the acetic acid formed in the degradation process.Studies have shown that the major volatile degradation product is aceticacid, with smaller amounts of ketene, water, methane, carbon dioxide andcarbon monoxide also being formed. Analysis of the degraded sample at400° C. shows a highly regular unsaturated material. The second step ofdegradation involves a dehydrogenation reaction.

Thus, there exists a need to provide a modified polymer having improvedproperties, such as increased melting point, while at the same timeproviding a use for excess sulfur.

SUMMARY

Generally, sulfur modified polymer compositions, free from asphalt,bitumen or like compounds, and methods of making same are provided.Specifically, sulfur modified polyvinyl acetate polymers are providedhaving increased melting points relative to the unmodified polymer.

In one aspect, a sulfur modified polyvinyl acetate polymer compositionis provided wherein the polymer composition includes a polyvinyl acetatepolymer; sulfur, wherein the sulfur is present in an amount up to about50% by weight; and wherein the composition is free from asphalt, bitumenor like compounds.

In certain embodiments, the sulfur is present in an amount between about10 and 20% by weight. In alternate embodiments, the sulfur is present inan amount between about 20 and 30% by weight. In alternate embodiments,the sulfur is present in an amount between about 30 and 40% by weight.In alternate embodiments, the sulfur is present in an amount betweenabout 40 and 50% by weight. In certain embodiments, at least a portionof the sulfur is present in elemental form. In certain embodiments, thesulfur modified polyvinyl acetate polymer composition has a meltingpoint that is up to 50° C. greater than the melting point of theunmodified polyvinyl acetate polymer. In certain embodiments, the sulfurmodified polyvinyl acetate polymer composition has a melting point thatis between 10° C. and 50° C. greater than the melting point of theunmodified polyvinyl acetate polymer. In certain embodiments, the sulfurmodified polyvinyl acetate polymer composition has a melting point thatis between 10° C. and 30° C. greater than the melting point of theunmodified polyvinyl acetate polymer. In certain embodiments, the sulfurmodified polyvinyl acetate polymer composition has a melting point thatis between 20° C. and 40° C. greater than the melting point of theunmodified polyvinyl acetate polymer. In certain embodiments, the sulfurmodified polyvinyl acetate polymer composition has a melting point thatis between 30° C. and 50° C. greater than the melting point of theunmodified polyvinyl acetate polymer.

In certain embodiments, the polyvinyl acetate polymer has a molecularweight of between about 10,000 and 25,000, alternatively between about25,000 and 75,000, alternatively between about 75,000 and 125,000.

In another aspect, a method for preparing a sulfur modified polyvinylacetate composition, free from asphalt, bitumen or like compounds, isprovided. The method includes the steps of providing a polyvinyl acetatepolymer, wherein the polyvinyl acetate polymer has a melting temperatureof less than about 140° C.; and heating the polyvinyl acetate polymer inthe presence of elemental sulfur to a temperature of between about 150°C. and 200° C. and mixing the polyvinyl acetate polymer and sulfur suchthat elemental sulfur is incorporated into the polyvinyl acetate polymerto produce a sulfur modified polyvinyl acetate polymer.

In certain embodiments, between about 40 and 50% by weight sulfur isincorporated into the polyvinyl acetate polymer In certain embodiments,between about 50 and 70% by weight sulfur is incorporated into thepolyvinyl acetate polymer. In certain embodiments, the polyvinyl acetatepolymer and sulfur are mixed for at least about 15 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a stress-strain curve comparing pure polyvinyl acetate andsulfur modified polyvinyl acetate.

FIG. 2 is a thermal analysis curve of sulfur.

FIG. 3 is a thermal analysis curve of a polyvinyl acetate sample.

FIG. 4 is a thermal analysis curve of a second polyvinyl acetate sample.

FIG. 5 is a thermal analysis curve of a sulfur modified polyvinylacetate sample.

FIG. 6 is a thermal analysis curve of another sulfur modified polyvinylacetate sample.

FIG. 7 is a thermal analysis curve of another sulfur modified polyvinylacetate sample.

FIG. 8 is a thermal analysis curve of another sulfur modified polyvinylacetate sample.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains many specificdetails for purposes of illustration, it is understood that one ofordinary skill in the art will appreciate that many examples, variationsand alterations to the following details are within the scope and spiritof the invention. Accordingly, the exemplary embodiments of theinvention described herein and provided in the appended figures are setforth without any loss of generality, and without imposing limitations,on the claimed invention.

Polyvinyl Acetate (PVAc) samples, free from asphalt, bitumen or likecompounds, of different molecular weights were modified using elementalsulfur. The sulfur modified polyvinyl acetate polymers showed increasedresistance to melting (i.e., increased melting point for the modifiedpolymer) and produced a softer polymer than the original, unmodifiedpolyvinyl acetate polymer. In general, polyvinyl acetate polymers wereselected that had a melting temperatures of less than about 140° C. Ingeneral, the addition and mixing of sulfur was performed at atemperature greater than the melting point of the polyvinyl acetatepolymer, for example in the range 150°-200° C. Alternatively, theaddition and mixing of sulfur can be performed in the range of about150-160° C., alternatively between about 160 and 170° C., alternativelybetween about 170 and 180° C., alternatively between about 180 and 190°C., alternatively between about 190 and 200° C. In general, thetemperature at which the sulfur addition and mixing take place ismaintained at a temperature that is below the decomposition temperatureof the polymer. Sulfur was added to the polyvinyl acetate polymer inamounts up to about 50% by weight of the polymer to produce modifiedpolymers having significantly different and unexpected mechanicalproperties, as compared with the pure polymers. In addition to theincrease in melting point of the modified polymer, the addition ofsulfur to the polyvinyl acetate polymers also produced a polymermaterial that was softer and more ductile in comparison with purepolyvinyl acetate polymers and showed no strain hardening like thehomopolymer. In certain embodiments, the addition and mixing of sulfurdescribed herein can be used for other polymers having similar meltingpoint ranges.

One advantage of the sulfur modified polymers is that the polymer canthen be produced at a highly competitive cost because sulfur is veryabundant and much cheaper than the polymer. This allows for the vastquantities of sulfur that are produced as a byproduct of oil and gasproduction to be utilized, thereby eliminating environmental concernsassociated with the storage thereof.

In certain embodiments, the sulfur modification of the polyvinyl acetatepolymer can result in an increase in the melting points of the polymersby more than 40° C. In certain embodiments, the addition of sulfur tothe polymer results in an increase of the melting point of the polymerby about 10° C., alternatively by about 20° C., alternatively by about30° C. In certain embodiments, the addition of sulfur to the polymerresults in an increase of the melting point of the polymer by about 50°C., or greater.

Further, the sulfur modified polyvinyl acetate polymer differs from thatof the unmodified polyvinyl acetate polymer because the sulfurcomposition becomes part of the polymer structure and at high content.The sulfur modified polymers can be used in adhesives and as an oilresistant polymer. In alternate embodiments, the sulfur modified polymerfinds use for use in crack repair of concrete structures.

EXAMPLES

Polyvinyl acetate polymers obtained from Scientific Polymer Products,Ontario, N.Y., USA were used as received. The technical specificationsof the polymers are provided in Table 1. Elemental sulfur (99.9% purity)from Saudi Aramco was used.

TABLE 1 Characterization of Polymers. Resin Product # Class of PolymerManufacturer T_(m), ° C. VA, % Mw Density g/cm³ PVAc1 1019 Polyvinylacetate Scientific Polymer  70* 100 15000 1.1700 PVAc2 347 Polyvinylacetate Scientific Polymer 105* 100 100000 1.1700 *softening temperatureas reported by the product data sheet

The sulfur modified polymers (SMP) were prepared in a Haake PolyDrivemelt blender. In an effort to include as much sulfur as possible intothe polymer blend, the composition of sulfur used was 50% and 70% byweight were employed. The Haake PolyDrive melt blender is designed foruse as a computer-controlled torque rheometer. The pure polymer andsulfur-polymer blends were mixed in the melt blender at 100 rpm forvarious different blend times. The blender thus acts as a batch stirredreactor with a constant volume. Samples were collected following themixing process and analyzed by different techniques. Blends ofPVAc1/sulfur, containing 50% by weight sulfur were prepared in the meltblender. The blending time, T_(m), was 10 minutes and reactiontemperature was 200° C. This sample preparation procedure was repeatedfor blend times, T_(m)=15 min and 20 min. The above procedure was alsorepeated using PVAc2 and PVAc1. The samples were prepared at differentprocessing times to investigate the effect of processing time on totalsulfur content and the amount of bonded sulfur in the SMP. Estimatingthe amount of total sulfur in the SMP was possible, however estimatingthe amount of bonded sulfur in the SMP was unsuccessful. Three blendsamples (PVAc1/S (50:50); PVAc1/S (30:70) and PVAc2/S (50:50)) wereprepared at processing time of 15 min.

A Vario EL elemental analyzer was used to determine the amount of freesulfur present in SMP. The thermal behavior of the pure resins andblends was determined by means of a TA Q1000 DSC. Samples of 7-10 mgwere weighed and sealed in aluminum hermetic pans. Melting temperaturemeasurements were performed by heating samples from room temperature to250° C. at a heating rate of 10° C./min, with a nitrogen purge gas at aflow rate of about 50 mL/min.

TABLE 2 Mechanical Properties of pure and sulfur modified PVAc PropertyPure PVAc PVAc + 50% Sulfur Young's Modulus (MPa) 4.31 1.93 YieldStrength (MPa) 21.51 9.05 % Elongation 68.32 30.84

As shown in Table 2, the addition of sulfur to the polyvinyl acetateresulted in a softer material which demonstated a drop in mechanicalproperties as the material started to elongate freely after the yieldpoint (no strain hardening behavior). Table 3 provides the results ofanalysis technique used to estimate total sulfur present in the SMP. Theresults closely match the actual amount of sulfur used in the blendingprocess. The SMP is not soluble in hot alcohol or hot acetone.

TABLE 3 % of Sulfur (S) in SMP. Sample S, Time Temp Total Measured No.ID Mw wt. % (min) (° C.) Sulfur (wt. %) 1 PVAc1 15000 50 10 200 55.9 2PVAc1 15000 50 15 200 53.4 3 PVAc1 15000 50 20 200 51.1 4 PVAc2 10000050 10 200 47.3 5 PVAc2 100000 50 15 200 49.8 6 PVAc2 100000 50 20 20050.4 7 PVAc1 15000 70 10 200 71.0 8 PVAc1 15000 70 15 200 69.5 9 PVAc115000 70 20 200 71.6 10 PVAc2 100000 70 10 200 73.0 11 PVAc2 100000 7015 200 70.9 12 PVAc2 100000 70 20 200 65.8

FIGS. 2-8 show the DSC melting thermograms of the pure sulfur, PVAc andseveral of the sulfur modified polyvinyl acetate blends. Pure sulfurexhibited two distinct peaks at approximately 106° C. and 122° C., asshown in FIG. 2, indicating the melting transition of two crystalconstituents. Pure PVAc1 (Mw=15000) shown in FIG. 3 shows a gradualsoftening transition as the temperature increases up to 150° C. PurePVAc2 (Mw=100000) shown in FIG. 4 display a strong peak at around 40° C.and a weak peak around 160° C. It is not believed that the weak peakcorresponds to the thermal degradation of PVAc, which is believed tooccur at above 227° C. FIG. 5 shows the DSC thermograms of severaldifferent blends of PVAc1/sulfur (having 50:50 compositions) prepared atdifferent blending times. A single melting peak around 120° C. for eachof the blends corresponds to the thermogram observed in the pure sulfurindicating the presence of sulfur in each of the blends. As shown inFIG. 6, increasing the sulfur content in the blend results in a similartrend wherein the thermograms of the various polymer blends show similarmelting peaks associated with the presence of free sulfur. As shown inFIGS. 7 and 8, the observed peaks correspond to those of sulfur and thepure polyvinyl acetate polymer sample, which may correspond to a newmaterial resulting from the reaction of sulfur and the polymer.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereupon without departing from the principle and scope of theinvention. Accordingly, the scope of the present invention should bedetermined by the following claims and their appropriate legalequivalents.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

Throughout this application, where patents or publications arereferenced, the disclosures of these references in their entireties areintended to be incorporated by reference into this application, in orderto more fully describe the state of the art to which the inventionpertains, except when these references contradict the statements madeherein.

As used herein and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

As used herein, terms such as “first” and “second” are arbitrarilyassigned and are merely intended to differentiate between two or morecomponents of an apparatus. It is to be understood that the words“first” and “second” serve no other purpose and are not part of the nameor description of the component, nor do they necessarily define arelative location or position of the component. Furthermore, it is to beunderstood that that the mere use of the term “first” and “second” doesnot require that there be any “third” component, although thatpossibility is contemplated under the scope of the present invention.

What is claimed is:
 1. A sulfur modified polyvinyl acetate polymercomposition, the polymer composition comprising: a polyvinyl acetatepolymer having a melting point of less than 140° C.; and sulfur, whereinthe sulfur is present in a range of 65.8% to 73% by weight, based on theweight of the polymer, such that the sulfur modified polymer has anincreased melting point as compared to the melting point of theunmodified polyvinyl acetate polymer.
 2. The polymer composition ofclaim 1, wherein the composition does not contain asphalt, bitumen, andcombinations thereof.
 3. The polymer composition of claim 1 wherein atleast a portion of the sulfur is present in elemental form.
 4. Thepolymer composition of claim 1 wherein the sulfur modified polyvinylacetate polymer composition has a melting point that is up to 50° C.greater than the melting point of the unmodified polyvinyl acetatepolymer.
 5. The polymer composition of claim 1 wherein the sulfurmodified polyvinyl acetate polymer composition has a melting point thatis between 10° C. and 50° C. greater than the melting point of theunmodified polyvinyl acetate polymer.
 6. The polymer composition ofclaim 1 wherein the sulfur modified polyvinyl acetate polymercomposition has a melting point that is between 10° C. and 30° C.greater than the melting point of the unmodified polyvinyl acetatepolymer.
 7. The polymer composition of claim 1, wherein the sulfurmodified polyvinyl acetate polymer composition has a melting point thatis between 20° C. and 40° C. greater than the melting point of theunmodified polyvinyl acetate polymer.
 8. The polymer composition ofclaim 1, wherein the sulfur modified polyvinyl acetate polymercomposition has a melting point that is between 30° C. and 50° C.greater than the melting point of the unmodified polyvinyl acetatepolymer.
 9. The polymer composition of claim 1, wherein the polyvinylacetate polymer has a molecular weight of between 10,000 and 25,000. 10.The polymer composition of claim 1, wherein the polyvinyl acetatepolymer has a molecular weight of between 25,000 and 75,000.
 11. Thepolymer composition of claim 1, wherein the polyvinyl acetate polymerhas a molecular weight of between 75,000 and 125,000.